The present invention generally relates to electronically tuned receivers, and more particularly to a television tuning system provided with a channel lockout feature to control viewer program selection.
The content of certain television programs has been found to be objectionable by some parents of young children. In order to prevent their children from viewing such programs, parents often supervise their children's use of the television by specifying those programs which can be viewed and/or the times during which the television can be operated. However, direct supervision may not always be possible or enforceable. As a result, various approaches have been proposed to inhibit or interefere with the reception of those channels on which the objectionable programs are broadcast or transmitted.
One approach is described in U.S. Pat. No. 4,232,396, which issued to A. S. Grimes. According to the Grimes patent, a plurality of individual circuits, each comprising at least one impedance element in series with a switch, is utilized. The individual series of circuits are all disposed in parallel and are connected to a single master switch in series therewith. Any one or more individual series circuit switches may be closed, and when the master series switch is closed, the impedance elements disposed in electrical relationship with one another either present a series impedance with the RF signal or shift the frequency of the local oscillator so as to preclude the receiver from operating on one or more selected channels. The user is thereby permitted to operate one or more individual channel disabling switches, either singly or in combination, such that when such switches are operated, and the master switch is also operated, those channels desired to be maintained inoperable are effectively disabled.
In another approach described in U.S. Pat. No. 4,317,213, issued to M. DiLorenzo, a device is connected to the television receiver to selectively interfere with the reception of selected channels. This device includes a number of signal generating circuits, each respectively set to generate a signal substantially equal to the carrier frequency of a corresponding television broadcast signal, and a timer which can be preset to activate and deactivate selected oscillations on a timed basis. The signal generating circuits are coupled to the antenna input leads of the television receiver so that when activated, the signals produced thereby cause sufficient interference with the corresponding incoming television broadcast signal to effectively block reception.
While the approaches taken by Grimes and DiLorenzo are effective to inhibit or interfere with the reception of those channels which are desired to be blocked, both require a substantial amount of additional hardware and either a modification of the television receiver or the connection of an external device to the television receiver. Also, it is noted that it is relatively easy to defeat or disconnect these systems. Therefore, it is apparent that what is still needed is a channel lockout feature for a television receiver which does not require substantial additional hardware and which is secure, i.e., cannot be easily defeated by someone not permitted to view the locked out channels.